1. Field of the Invention
The present invention concerns an avionic tray.
2. Description of the Prior Art
Avionic equipment is housed in standard size cases. There are various standard case sizes of various widths. Each case is an interchangeable removable modular unit which is placed in a tray. The tray has latches at the front which attach to fixing lugs on the case and at the rear of the case is an electrical connector which plugs into a complementary connector fixed to the rear of the tray. The trays are fixed side by side along shelves.
The present invention concerns a tray of this kind. Given their use in aerospace applications, they must be light in weight. They are therefore made from thin aluminum. The standard thickness is 1.6 mm. The trays are subject to high mechanical loads, however, and so must be strong and resistant to metal fatigue. Some parts of the tray are therefore reinforced, in particular the front and rear parts of the base plate of the tray where it is screwed to the shelf.
The appended FIG. 1 is a partial perspective view of the front part of a known type tray 1. The bottom or base plate 2 of the U-shape tray front part is reinforced underneath by a reinforcement plate 3 riveted and/or spot welded to the base plate 2 of the tray. The tray 1 is fixed to the shelf 4 by screws 5. The screwheads must be flush to allow insertion of the equipment case. The screws are therefore countersunk and are accommodated in a countersink 6 at the upper end of the screw hole 7. An alternative is to stamp a well to accommodate the screwhead.
This arrangement is satisfactory in terms of increasing the stiffness of the tray but is not satisfactory with respect to resistance to metal fatigue caused by vibration, and cracks appear at the edges of the holes through which the screws fixing the tray to its shelf pass. As already mentioned, the metal of the tray is thin and the thickness is reduced around the fixing screw holes by the countersink to accommodate the screwhead. In the case of a stamped housing for the screwhead, this area is also more fragile. The fixing of the reinforcing plate 3 to the bottom of the base plate 2 of the tray 1 is not an intimate fixing over all of the reinforcement surface but rather a fixing at individual points (spot welds and/or rivets, as mentioned above). When the tray is subject to transverse loads the reinforcement plate 3 under the base plate 2 takes much less of the load than the base plate which is directly under the screwheads. As already mentioned, this causes cracks to appear at the edges of the screw holes in the base plate 2.
An object of the present invention is to overcome this drawback.